The invention relates to a separator for separating liquid droplets from an aerosol, and relates in particular to an oil separator for the crankcase ventilation gases of a reciprocating internal combustion engine, comprising a rotor arranged in a stationary housing and capable of being driven in rotation about a rotor axis, said rotor comprising a plurality of disks which are concentric with the rotor axis and are arranged parallel to one another, said disks together forming a stack of disks capable of being driven in rotation about the rotor axis and being arranged at in particular equal distances relative to one another in a direction of the rotor axis, a gas flow path between a dirty gas inlet of the separator for a gas entraining liquid droplets to be separated and a clean gas outlet of the separator for the gas cleaned, at least to a large extent, of the liquid droplets, a liquid outlet for discharging separated liquid from the housing, and an annular space between the circumference of the rotor and a circumferential wall of the housing enclosing the rotor, wherein the liquid outlet is in communication with the annular space and disks adjacent to each other in each case form therebetween an interspace that is concentric with the rotor axis and through which the gas is to flow, the radially outer area of said interspace opening into the annular space, and wherein one of the dirty gas inlet and the clean gas outlet is in communication with the annular space and the other one of the dirty gas inlet and the clean gas outlet is in communication with radially inner areas of the interspaces.
Such a separator, having its rotor disk stack formed by conical, namely frusto-conical disks, is known from WO 01/36103 A. As shown in FIG. 1 of said document, all of the frusto-conical disks are arranged along the rotor axis at such distances from one another that their cone angle opens out in the same axial direction and disks adjacent to each other interengage in an axial direction such that when seen in a radial direction the frusto-conical areas of disks adjacent to each other overlap to the largest extent. As is apparent from FIG. 1, the separation action of this known separator relies on the following principle: As the rotor rotates and when the gas to be cleaned flows through the interspaces between the disks adjacent to one another, liquid droplets entrained by the gas to be cleaned are thrown against the inner wall surfaces of the conical disks due to the centrifugal forces to which they are subjected, whereby liquid droplets are separated out on these inner wall surfaces, forming liquid films thereon which are transported to the outer circumference of the rotor by the centrifugal forces, whereupon the separated liquid is spun off the rotor radially outwardly therefrom, thereby at least in part impacting against the circumferential wall of the housing. From the annular space between the rotor and the housing and from the housing's circumferential wall, the separated liquid is then carried by gravity into the housing lower portion and leaves the housing via the liquid outlet thereof.
As is apparent from the section taken along line 2-2 of FIG. 1, depicted in FIG. 2, the inner (i.e. in FIG. 1 upper) wall surfaces of the cone-shaped disks have ribs arranged thereon which, as seen in a direction of the rotor axis, are curved in the shape of a crescent and whose purpose and mechanism of action are apparent from page 12, lines 22 to 26 of WO 01/36103 A: Liquid droplets that have been separated out on the conical inner wall surfaces of the disks in the above-described manner are captured by and conducted along these ribs towards the outer circumference of the disks, with the separated liquid droplets coalescing into larger droplets or amounts of liquid which are then spun off the rotor. The ribs act as flow guiding elements for partial gas streams formed by the gas flowing through the interspaces between disks adjacent to one another, and consequently when seen in a direction of the rotor axis the flow paths for the partial gas streams extending between the ribs take a curved shape (see p. 11, lines 19 to 21). However, according to the basic principle of this known separator, the liquid droplets to be separated are exclusively or at least for the most part separated out on the conical inner surfaces of the disks and only then reach the ribs, where they accumulate and coalesce to form larger droplets or amounts of liquid (see in particular claim 1, namely p. 16, lines 15 to 17 and 26 to 30, and p. 5, lines 2 to 5 and 7 to 11).
For the cleaning of what are known as blow-by gases as occur in reciprocating internal combustion engine crankcase ventilation, powered separators such as separators of the kind defined at the outset are used in the commercial vehicle field, whereas for smaller engines as are employed in passenger cars, passive separators are used, more recently separators in particular whose separating system is formed by a combination of an impactor (impaction plate or the like) and a non-woven fibrous material. However, the relatively high pressure loss in the gas stream of the blow-by gases that is caused by the presence of such passive separators may be disadvantageous and the separation efficiency of such passive systems on material in the ultra-fine droplet range with droplets sized approximately 0.7 μm or less is in need of improvement; any improvement in this regard has heretofore required the use of powered separators, in particular separators of the kind as are apparent from WO 01/36103 A. However, as a result of the conical shape of their disks, these known separators have a relatively large axial overall length relative to the number of disks required for the desired separation efficiency, this being perceived as a disadvantage, in particular where passenger cars are concerned, and reducing the axial overall length by reducing the number of disks has a detrimental effect on the separation performance of such separators. Moreover, known separators as are apparent from WO 01/36103 A are very sensitive to variations with time of the magnitude of the volumetric flow rate of the gases to be cleaned.
Therefore, the object underlying the invention is to propose an improved separator of the kind defined at the outset which has, in principle, a better separation performance for the same overall size and under the same operating conditions than has a separator provided with conical disks.